In recent years, information technology-related devices and communication devices such as personal computers, video cameras, and mobile phones have rapidly become popular, and therefore importance is placed on the development of batteries (e.g., lithium batteries) excellent as power sources of such devices. Further, in industrial fields other than the fields of information technology-related devices and communications-related devices, for example, in the field of automobile industry, lithium batteries and the like for use in electric cars and hybrid cars are being developed.
Conventional commercially-available lithium batteries use an organic liquid electrolyte containing a flammable organic solvent, and therefore need to have a safety device that suppresses temperature rise during short circuit and to be improved in structure and material to prevent short circuit. On the other hand, solid state batteries using a solid electrolyte instead of a liquid electrolyte have no flammable organic solvent therein, and therefore their safety devices can be simplified. For this reason, it is believed that solid state batteries are advantageous in production cost and productivity.
In the field of such solid state batteries, a powder-form sulfide solid electrolyte material is conventionally known. Such a sulfide solid electrolyte material has excellent ion conductivity, and is therefore used as a material for forming a solid electrolyte layer between a cathode layer and an anode layer, or is added to a cathode layer and an anode layer to improve ion conductivity. However, such a powder-form sulfide solid electrolyte material has a problem that its workability and moldability are poor.
In order to solve such a problem, attempts have been heretofore made to form a sheet-shaped solid electrolyte by adding a binder composition to a sulfide solid electrolyte material. For example, Patent Document 1 discloses a solid electrolyte sheet obtained by using, as a binder composition for a sulfide solid electrolyte material, a two-component binder composition curable by addition reaction (thermal addition polymerization) (see Example 4 in Patent Document 1). This binder composition exhibits bindability by polymerizing a silicone monomer by thermal addition polymerization. Further, Non-Patent Document 1 discloses the use of a silicone rubber, obtained by cross-linking a cross-linkable liquid silicone by thermal addition polymerization, as a binder for a sulfide solid electrolyte material. Such thermal addition polymerization utilizes a hydrosilylation reaction, and usually uses a hydrosilylation catalyst (e.g., Pt catalyst).
Further, Patent Document 2 discloses selective cross-linking of an unsaturated double bond-containing liquid rubber, in which a hydrosilylation catalyst is uniformly dispersed, with the use of a silicone compound having a hydrosilyl group. Further, Patent Document 3 discloses the use of a butadiene rubber as a binder for a sulfide solid electrolyte material.
Patent Document 1: Japanese Patent Application Laid-open No. 2008-021416
Patent Document 2: Japanese Patent Application Laid-open No. Hei 9-227604
Patent Document 3: Japanese Patent Application Laid-open No. Hei 11-086899
Non-Patent Document 1: Taro Inada et al., “Fabrications and properties of composite solid-state electrolytes”, Solid State Ionics 158 (2003) 275-280